<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        #test{
            width: 100px;
            height: 100px;
            background-color: red;

            /* 边框实现 border:width style color */
            border: 2px solid blue;

            /* 固定宽度元素居中 margin */
            margin:0px auto; 
        }
        #test2{
            width: 0;
            height: 0;
            margin: 0 auto;

            /* 上下左右边框宽度为50 */
            border:50px solid blue;

            /* 设置底部和左右边框颜色为透明 */
            border-bottom-color: transparent;
            border-left-color: transparent;
            border-right-color: transparent;
        }
        #test3{
            /* 实现一个圆的步骤 */
            width: 100px;
            height: 100px;
            background-color: green;
            margin: 0 auto;
            border: 2px solid transparent;
            border-radius: 50%;
        }
        input{
            /* 取消轮廓线 */
            outline: none;
        }
    </style>
</head>
<body>
    <!-- <div id="test">
        
    </div>
    <div id="test2">

    </div>
    <div id="test3">

    </div> -->
    <input type="text">
    <input type="submit" value="提交">
    <input type="button" value="操作">
</body>
</html>